Biochemical properties and hydrolytic activity in the nutria (Myocastor coypus) digestive tract

Abstract

Current understanding of site-specific digestion of carbohydrates in mammals is that whereas starch can be degraded by mammalian enzymes, other complex carbohydrates (e.g. pectin, inulin, xylan or cellulose) are typically digested by the enzymes of symbiotic microbes. To test whether the previously reported presence of complex carbohydrate-digesting enzymes in the small intestine of sheep represent actual small intestinal enzyme activity or just outflux of microbial enzymes from the forestomach, we applied the same methodology of isolating enzymes from gastrointestinal contents and applying them in vitro to test substrates in nutria (Myocastor coypus), a hindgut-fermenting rodent without a forestomach. No enzymatic activity against carbohydrates was detected in the stomach, excluding an effect of coprophagy on the presence of the investigated enzymes. While – as expected – starch digestion was highest in the small intestine, and that of the other carbohydrates was highest in the caecum, there was nevertheless detectable enzymatic activity against pectin, inulin, xylan and cellulose in the small intestine. Further investigations notwithstanding, we suggest that these results indicate a certain degree of unspecific carbohydrase activity by small intestinal enzymes that plays no relevant role in vivo due to the short residence time of digesta in the small intestine.